Statistical Modeling of Single-Photon Avalanche Diode Receivers for Optical Wireless Communications

In this paper, a comprehensive analytical approach is presented for modeling the counting statistics of active quenching and passive quenching single-photon avalanche diode (SPAD) detectors. It is shown that, unlike ideal photon counting receiver for which the detection process is described by a Poisson arrival process, photon counts in practical SPAD receivers do not follow a Poisson distribution and are highly affected by the dead time caused by the quenching circuit. Using the concepts of renewal theory, the exact expressions for the probability distribution and moments (mean and variance) of photocounts in the presence of dead time are derived for both active quenching and passive quenching SPADs. The derived probability distributions are validated through Monte Carlo simulations and it is demonstrated that the moments match with the existing empirical models for the moments of SPAD photocounts. Furthermore, an optical communication system with on-off keying and binary pulse position modulation is considered and the bit error performance of the system for different dead time values and background count levels is evaluated

Statistical modeling of single-photon avalanche diode receivers for optical wireless communications

In this paper, a comprehensive analytical approach is presented for modeling the counting statistics of active quenching and passive quenching single-photon avalanche diode (SPAD) detectors. It is shown that, unlike ideal photon counting receiver for which the detection process is described by a Poisson arrival process, photon counts in practical SPAD receivers do not follow a Poisson distribution and are highly affected by the dead time caused by the quenching circuit. Using the concepts of renewal theory, the exact expressions for the probability distribution and moments (mean and variance) of photocounts in the presence of dead time are derived for both active quenching and passive quenching SPADs. The derived probability distributions are validated through Monte Carlo simulations and it is demonstrated that the moments match with the existing empirical models for the moments of SPAD photocounts. Furthermore, an optical communication system with on-off keying and binary pulse position modulation is considered and the bit error performance of the system for different dead time values and background count levels is evaluated

The Bit Error Performance and Information Transfer Rate of SPAD Array Optical Receivers

In this paper the photon counting characteristics, the information rate and the bit error performance of single-photon avalanche diode (SPAD) arrays are investigated. It is shown that for sufficiently large arrays, the photocount distribution is well approximated by a Gaussian distribution with dead-time-dependent mean and variance. Because of dead time, the SPAD array channel is subject to counting losses, part of which are due to inter-slot interference (ISI) distortions. Consequently, this channel has memory. The information rate of this channel is assessed. Two auxiliary discrete memoryless channels (DMCs) are proposed which provide upper and lower bounds on the SPAD array information rate. It is shown that in sufficiently large arrays, ISI is negligible and the bounds are tight. Under such conditions, the SPAD array channel is precisely modelled as a memoryless channel. A discrete-time Gaussian channel with input-dependent mean and variance is adopted and the properties of the capacity-achieving input distributions are studied. Using a numerical algorithm, the information rate and the capacity-achieving input distributions, subject to peak and average power constraints are obtained. Furthermore, the bit error performance of a SPAD-based system with on-off keying (OOK) is evaluated for various array sizes, dead times and background count levels

Single-photon avalanche diode receivers for optical wireless communications

Single-photon avalanche diodes (SPADs) have been widely applied in many applications over the past few decades thanks to their high sensitivity, high photon detection efficiency and high timing resolution. Nowadays, they are drawing particular attention in the field of optical wireless communication (OWC), resulting in wider and deeper studies among the scientific research community. Compared with positive-intrinsic-negative (PIN) diodes and avalanche photodiodes (APDs), SPADs provide much higher internal gains and sensitivities, thereby easily overcoming the thermal noise and enabling the detection of individual photons without the need for transimpedance amplifiers (TIAs). However, upon detecting a photon, the SPAD is unable to respond to subsequent incident photons for a certain period of time, called dead time. This dead time is caused by the quenching circuit, which is of two principal modes: active quenching (AQ) and passive quenching (PQ). Depending on the structure of this circuit, the dead time can be constant or variable, in any case, it degrades the photon counting performance of the SPAD. In this thesis, a comprehensive analytical approach is presented for modelling the counting statistics of SPAD detectors in the presence of dead time. To the best of author’s knowledge, this is the first in-depth study of the impact of dead time in the context of OWC. Using the concepts of arrival processes and renewal theory, the exact photocount distributions and the count rate models are derived for AQ and PQ single SPADs. It is shown that, unlike ideal photon counting detectors, in AQ and PQ single SPADs, the photocounts do not follow a Poisson distribution. The results confirm that AQ single SPADs generally exhibit less counting losses and therefore, higher count rates compared to PQ single SPADs and the count rate gap in high photon rate regimes is substantial. It is also shown that the photocount distribution of a SPAD array can be well approximated by a Gaussian distribution, for which the mean and variance are dead time dependent. The numerical results suggest that as the size of the array increases, the gap between the photon counting performance of AQ and PQ SPAD arrays tends to vanish. Furthermore, in this thesis, the bit error performance of SPAD-based OWC systems with AQ single SPADs, PQ single SPADs and AQ SPAD arrays are evaluated. The results show that the SPAD dead time significantly degrades the bit error ratio (BER) of the systems. The system with an AQ single SPAD exhibits better BERs compared to the system with a PQ single SPAD. The effect of dead time is mitigated to some extent when an array is employed. The analytical and Monte Carlo simulation results are provided for various dead time values, background count levels and SPAD array sizes. From a communication theory point of view, the dead time also limits the achievable data rate of SPAD-based systems. In this thesis, the information transfer rate of SPAD detectors is also investigated. To this end, the SPAD is modelled as a communication channel. Using an information theoretic approach, the channel capacity and the capacity-achieving input distributions for AQ single SPADs and AQ SPAD arrays are obtained for various dead time values, background count levels, and array sizes

SPAD-Based Optical Wireless Communication with Signal Pre-Distortion and Noise Normalization

In recent years, there has been a growing interest in exploring the application of single-photon avalanche diode (SPAD) in optical wireless communication (OWC). As a photon counting detector, SPAD can provide much higher sensitivity compared to the other commonly used photodetectors. However, SPAD-based receivers suffer from significant dead-time-induced non-linear distortion and signal dependent noise. In this work, we propose a novel SPAD-based OWC system in which the non-linear distortion caused by dead time can be successfully eliminated by the pre-distortion of the signal at the transmitter. In addition, another system with joint pre-distortion and noise normalization functionality is proposed. Thanks to the additional noise normalization process, for the transformed signal at the receiver, the originally signal dependent noise becomes signal independent so that the conventional signal detection techniques designed for AWGN channels can be employed to decode the signal. Our numerical results demonstrate the superiority of the proposed SPAD-based systems compared to the existing systems in terms of BER performance and achievable data rate

Employing VLC technology for transmitting data in biological tissue

Abstract. With the development in wireless communication methods, visible light communication (VLC), a subset of Optical Wireless Communication (OWC) has garnered much attention to employ the technology for a secure short-range wireless communication. We present a feasibility study to determine the performance of VLC in short range wireless transmission of data through biological tissue. VLC is a cost efficient and secure means of transmitting high volume of data wirelessly which can considerably reduce the interference issues caused by electromagnetic pulses and external electric fields. We present a simple measurement approach based on Monte Carlo simulation of photon propagation in tissue to estimate the strength of wireless communication with body implant devices. Using light for communication brings inherent security against unauthorized access of digital data which could be acquired from the low energy body implant devices used for medical diagnosis and other studies. This thesis discusses the typical components required to establish VLC such as, transmitter, receiver and the channel mediums. Furthermore, two cases of Monte Carlo simulation of photon-tissue interaction are studied to determine a possibility if VLC is a suitable substitute to radio frequency (RF) for a more wireless communication with the body implants. The process of theoretical measurement begins with conversion of light intensity into an electrical signal and an estimation of achievable data rate through a complex heterogeneous biological tissue model. The theoretically achieved data rates of the communication were found to be in the order of megabits per second (Mbps), ensuring a possibility to utilize this technology for short range reliable wireless communication with a wider range and application of implant medical devices. Biophotonics.fi presents a computational simulation of light propagation in different types of computational tissue models comprehensively validated by comparison with the team’s practical implementation of the same setup. This simulation is also used in this thesis (5.2.2) to approximate more accurate data rates of communication in case of a practical implementation

Broadband optical wireless communications for the teleoperation of mining equipment

The current level of technological advancement of our civilization serving more than seven billion human population requires new sources of biotic and abiotic natural resources. The depletion and scarcity of high-grade mineral deposits in dry land are forcing the Natural Re- sources industry to look for alternate sources in underwater environments and outer space, requiring the creation of reliable broadband omnidirectional wireless communication systems that allows the teleoperation of exploration and production equipment. Within these ob- jectives, Optical Wireless Communications (OWC) are starting to be used as an alternative or complement to standard radio systems, due to important advantages that optical wave- lengths have to transmit data: potential for Terabit/s bit rates, broadband operation in underwater environments, energy e ciency and better protection against interference and eavesdropping. This research focus in two crucial design aspects required to implement broadband OWC systems for the teleoperation of mining equipment: high bandwidth wide beam photon emission and low noise omnidirectional Free-Space Optical (FSO) receivers. Novel OWC omnidirectional receivers using guided wavelength-shifting photon concentra- tion are experimented in over 100 meters range vehicle teleoperation.Master of Science (MSc) in Natural Resources Engineerin